1. Field of the Invention
The present invention relates to a method of and apparatus for treating and conditioning fluids. More particularly, the present invention relates to a method of and apparatus for treating and conditioning fluids, including liquids, gases and fluidized solids, using catalyzed hydrodynamic cavitation. The invention alters selected physical and chemical characteristics of selected components present in the fluids to catalyze desirable chemical reactions between constituents of the fluid and to encourage ionization of the fluids, facilitating the removal of harmful contaminants from the treated material. The invention is applicable to the beneficial treatment of many fluid systems, including the purification of water, enhanced recovery of crude oil, desulphurization of hydrocarbons, remediation of contaminated soil and the prevention of scale and corrosion.
2. Background
All industrial processes, water treatment operation and processes used to recover and utilize natural resources depend at some point upon the successful removal of undesirable contaminants or the recovery of desirable materials from fluids. The fluids referred to may be liquids, gases or slurries and the material separated from the fluids may be any material dissolved, emulsified suspended or solubilized in the fluid. The commonly known techniques for separating solids, liquid particles or gases from fluids include the following:
Filtration. Filtration usually refers to the use of granular media, filter cartridges or bag filters to remove suspended solids greater than 1 micron from fluids. Fluids are pumped through the filter material which strains out the suspended solids from the fluid. Filtration is effective where the solids are not emulsified or dissolved in the fluid. Filter media eventually becomes blinded off by the bulk of the collected particles, inhibiting the flow of fluid through the media, and must be cleaned by backwashing or the media must be replaced. Certain solids, such as iron sulfite, biomass and solidified hydrocarbons are difficult to filter because they form a slimy film over the filter media, blocking passage of the fluid through the media. Filtration is one of the most common industrial processes and filtration systems are employed in all fluid treatment applications. Filtration isn't an effective means to removed dissolved solids from fluids.
Precipitation. Precipitation is usually a chemical process whereby acids, bases or chelating compounds are added to a fluid in order to reduce the solubility of a contaminant in the fluid. Precipitation depends upon the solubility of the material in the fluid, the charge of the compound, temperature of the fluid and time. Chemicals must be added to the fluid and the resulting precipitate must then be separated from the fluid by some other appropriate method. The pH of the fluid may also have to be adjusted after the solids are removed. Precipitation is a useful way to removed dissolved solids from a fluid but may not always be economical because of the cost of the chemical used to facilitate the precipitation of the solids.
Decanting. Liquids having different specific gravities, i.e., oil and water, can be separated by allowing them to stand in a settling tank. The lighter liquid floats to the top of the heavier liquid and can be skimmed off. Decanting isn't instantaneous and time is required for the two liquids to separate. Skimming is usually inefficient and the two liquids are often not completely separated. Typically skimmed oil contains about 15% water and the separated water contains around 50 parts oil per million parts water. Skimming is not effective for removal of dissolved solids.
De-emulsification. Emulsions are intimate mixtures of two liquid phases, such as oil and water, in which the liquids are mutually insoluble and where either phase may be dispersed in the other. It is difficult to separate emulsified liquids. Stable oil-water emulsions are a colloidal system of electrically charges oil droplets surrounded by an ionic environment. Emulsions often contain suspended solids and other contaminants that cannot be separated from the fluid because of the emulsion. De-emulsification involves adding chemicals, typically strong acids and metal salts, to the fluid to add a positive charge to the emulsion droplets in order to neutralize their negative charges and cause the droplets to loose their attraction to each other. Once the liquid phases are neutralized, the two phases can be allowed to separate by settling or by coalescing processes. The pH of the one or more of the liquids in the fluid a may also have to be adjusted and the chemical de-emulsifiers may have to be removed after separation.
Ion-Exchange. Ion exchange removes contaminants from fluids by transferring them to a solid material that has affinity for the contaminants. The solid material, typically called ion exchange media or resin, accepts the contaminants and exchanges them for an equivalent amount of material stored in the ion exchange material. By this process, undesirable contaminants are exchanged for presumably beneficial or benign chemical compounds. Ion exchange is useful for the removal of dissolved solids from fluids when the fluid is not adversely affected by the presence of the new material. Ion Exchange media must be regenerated when all of the exchange sites are depleted. Ion exchange media is often quite expensive and ion exchange process are often undesirable because materials exchanged from the media may in themselves become new contaminants.
Degasification. Fluids may contain a variety of gases in solution that contaminate the fluid and are difficult to remove without specific degassing processes. Gases are held in solution in proportion to the partial pressure of the gas in the vapor space above the fluid/gas interface. Gases are removed by reducing the surface tension of the fluid and increasing the rate of diffusion of the gas through the fluid. Degasification processes typically involve atomization of the fluid in stripping towers, mechanical agitation of the fluid to shear the gas from the liquid or heating the fluid to increase gas diffusivity. Chemical agents that reduce the surface tension of the fluid are also used to facilitate the removal of dissolved gases. Equipment used for this purpose is expensive to build and operate, and many fluids are degraded by the addition of heat used to decrease the solubility of the gasses in the fluid.
Adsorption. Adsorption is the physical adhesion of molecules, especially organic molecules or colloids to the surfaces of the adsorbent material. Adsorption is particularly useful for removal of dissolved solids of high molecular weight. Like ion exchange, adsorption processes use media such as activated carbon for adsorption that has limited capacity and must be replaced periodically. Adsorption is not a cost-effective process for many fluid purification applications because of the high cost of the adsorption media and the problems and costs associated with disposal of the spent media now saturated with contaminants.
Membrane Separation. Membranes are porous barriers that will allow selected fluids to pass through while forming a barrier to particulates and dissolved solids. Fluid is pushed through the membrane by a pump or a compressor. A type of membrane process, reverse osmosis, is very useful for purifying water. Membranes are expensive and have to be replaced frequently because of degradation and because they are susceptible to fouling from biological organisms. Membranes also create a concentrated waste containing the contaminates that often must be disposed of as a hazardous waste material.
Centrifugation. Liquid or solid particles having higher specific gravities than the bulk fluid base can be separated by centrifugation. Here the heavier material is physically separated from the lighter material by centrifugal forces. Due to the weight of the fluid and the dynamic vibrations incurred, the centrifuges are both massive and expensive to operate.
Coagulation and Flocculation. Coagulation and flocculation are employed to separate suspended solids, particularly colloidal particles, from fluids. The process works by using chemicals to neutralize the negative charge on the surface of the particles and reduce the forces, as measured by the zeta potential of the particles, that keep the particles from agglomerating together. The process must occur in a slow mixing environment to allow enough time for agglomeration and settling of the particles out of the fluid. Flocculation takes time to allow the particles to settle and is effective for only a narrow range of particles. Coagulation and flocculation are usually ineffective to removed dissolved solids, separate emulsions or to separate hydrocarbons from water and other polar liquids. Once the particles are removed the fluid must be further purified by filtration or another similar operation.
Distillation. This method involves boiling the liquid and condensing the vapor. Distillation requires massive amounts of energy and is inefficient when the specific gravities of the liquid base and the solid or liquid particles are close together.
Coalescing Processes. Liquids having different specific gravities, i.e., oil and water, can be separated more rapidly when processed through a coalescer. The coalescing media forces small oil droplets suspended in the polar fluid to agglomerate together to form large droplets that more easily separate from the bulk fluid. The lighter hydrocarbons can then be skimmed off of the bulk fluid. Coalescers are not effective for conditioning fluids to prevent scale formation or for the removal of dissolved solids.
Oxidation Reduction. Oxidation-reduction processes, or Redox processes, are used to chemically change the nature of a contaminant in a fluid so that it can be more easily removed by mechanical separation operations or by precipitation. Chemicals are added to a fluid to either oxidize or reduce a contaminant, changing soluble ionized compounds into stable and insoluble complexes. Redox processes involve the transfer of electrons between compounds, frequently within electrolytic cells. Oxidation-reduction processes that depend upon the addition of chemicals to remove contaminants are often not cost-effective because of the cost of the chemicals.
Electrostatic Precipitation. Electrostatic precipitation processes are similar to Redox processes in that a charged surface is created that has an affinity for positively charged contaminants. The use of an electrochemical processes to clarify and purify waste water streams is described in U.S. Pat. No. 6,238,546 issued to Kneiper whereby a pair of electrodes are immersed in the fluid in a treatment chamber and DC current is passed through the fluid between the electrodes. The process is reported to induce a static charge on the waste particles in the fluid, inducing them to coalesce and agglomerates. The equipment used to generate the electric charge in the fluid is usually quite expensive to purchase and operate.
Redox Media. Specialized water conditioning media, called Redox media, can also be used to condition and ionize fluids that passes through the media. Redox cells and Redox media are structured so that one component of the cell or media acts as an anode and the other component acts as the cathode. In the presence of a fluid, electrons flow from the anode to the cathode thereby becoming available to react with positively charged contaminants in the fluid, causing them to plate out on the anode and be removed from the fluid. Redox media and its uses are described in U.S. Pat. No. 5,559,456, entitled “Fluid Treatment Utilizing a Reticulated Foam Structured Media Consisting of Metal Particles;” and U.S. Pat. No. 5,757,400, entitled “Reticulated Foam Structured Fluid Treatment Element.” issued to Fanning and Garret.
Many other new processes have been proposed to remove contaminants or recover materials from fluids. These processes are in some cases experimental or unproven. The most promising of these new processes include cavitation and fluid ionization:
Cavitation. A practical definition of cavitation is the formation and collapse of vapor cavities in a flowing liquid. These vapor cavities can form anywhere in a flowing liquid where the local pressure is reduced to that of the liquid vapor pressure at the temperature of the flowing liquid. (Perry's Chemical Engineer's Handbook, 6th Edition 1984, McGraw-Hill) Cavitation is a physical condition whereby bubbles and cavities within a fluid are created by a localized pressure drop in the fluid. The low pressure zones are produced by local increases in fluid velocity as in eddies or vortices and can be caused by a propeller blade moving at great speed though a fluid, by an impeller operating at a high rpm in a fluid or by movement of a fluid through a restriction or a nozzle. Cavitation can also be generated in a fluid by the application of ultrasound energy.
Fluid exposed to these conditions may undergo a dramatic decrease in pressure to the point whereby the liquid reaches its boiling point, creating a great number of vapor-filled cavities and bubbles. The pressure drop is typically very short in duration and when the bubbles are projected further into the bulk of the liquid an equally dramatic increase in pressure imposed from the bulk fluid causes the collapse of the bubbles and the void spaces. According to some studies, the rapid expansion and collapse of the bubbles brought about by the cavitation pressure impulses have been shown to expose fluids to extremely high localized temperatures and pressures, with temperatures reportedly as high as 5,000 degrees Kelvin and pressures as high as 500 kg/cm (K. S. Suslick, Science, Vol. 247, 23 March 1990, pgs 1439–1445).
Cavitation is usually an uncontrolled and destructive condition but cavitation processes are reportedly useful for water purification and the destruction of hazardous wastes. Suslick describes a process called hydrodehalogenation whereby MoC catalysts were prepared by a sonication cavitation procedure and used to remove Cl and F from halogenated hydrocarbons when both catalyst and halogenated hydrocarbons were processes through a cavitation reactor. The localized hot-spots created during cavitation are reported to be able to strip ligands away from metal complexes. (K. S. Suslick, Published DOE Report under DOE Award DEFG07-96ER14730, 21 November 1997)
Hydrodynamic cavitation is a variation of generalized cavitation that occurs during turbulent fluid flow and is characterized by large pressure differences that are generated within the turbulent fluid. Hydrodynamic cavitation is usually an uncontrolled and undesirable condition brought about by constricted flow of fluids through an orifice or a nozzle or by operation of a pump to transfer a mixture of gas and liquid.
Some processes, as described in U.S. Pat. No. 6,365,555 by Moser and other related patents, are reported to be able to control hydrodynamic cavitation in order to enhance mixing and promote chemical reactions in fluids. Cavitation is typically controlled through the use of sonication devices that impose controllable and measurable amount of force upon the fluid or by the use of specially designed nozzles that direct the flow of fluid undergoing cavitation in a controlled manner. Processes designed by Moser and others use controlled cavitation to create nanometer sized reaction products, typically nanometer sized particles of catalyst material, superconductors, pigments and specialized materials.
Fluid Ionizers. Fluid ionizers are allegedly able to separate immiscible particles from liquid mixtures or emulsions. The ionizers, also described as Ion Colliders by some references, operate by directing a stream of liquid under pressure which contains solid or liquid immiscible particles against the surface of a metal plate to induce the metal to give up electrons which then combine with the liquid molecules and with the particle molecules causing the similarly charged liquid and particles to repel and separate from each other. Fluid ionizers claim to purify fluids by ionizing the fluid and impinging the fluid against a catalytically active metal surface. The ionizer apparatus typically rely upon the principles of cavitation of a fluid through channels in the apparatus to force a jet or stream of the cavitation-induced bubbles of vaporized fluid to impinge upon a catalytically active metal surface. The cavitation-induced bubbles then collapse at the catalytically active metal surface, generating high temperatures and pressures at the catalyst surface that are reported to produce physical and chemical changes in the fluid.
One type of fluid ionizer, called an Ion Collider and described in U.S. Pat. Nos. 5,482,629 and 6,106,787 by Rippetoe specifiy the use of copper and nickel as the preferred metals for the collider surface since copper reportedly readily gives up electrons in the presence of nickel when bombarded by a stream of liquid. The Rippetoe collider consists of two spaced apart concentric metal cylinders or pipes where either both pipes are made of copper-nickel alloy or preferably both the inner surface of the outer cylinder and the outer surface of the inner cylinder are coated with a copper-nickel alloy. The wall of the inner cylinder contains a multiplicity of spaced apart radially bored holes and the exit end of the inner cylinder is capped. The opposite or entry end of the inner cylinder may have a filter screen to prevent entry into the Ion Collider of gravel or other large particles. The liquid is pumped under pressure into the inner cylinder causing a multiplicity of streams or jets to issue from the inner cylinder wall and bombard the inner surface of the copper-nickel wall of the outer cylinder. Electrons freed from the copper in the walls of the annular chamber between the two cylinders combine with both molecules in the base fluid and the particles, causing the particles to separate from the base fluid. Rippetoe patented the use of the Ion Collider for a number of applications including separation of emulsions; purification of water; enhanced recovery of crude oil; and the remediation of contaminated soil.
In U.S. Pat. No. 5,482,620, Rippetoe describes the use of the Ion Collider as a method and apparatus for separating immiscible solid or liquid particles such as oil from a liquid-based mixture or emulsion. The apparatus is as shown above. In U.S. Pat. No. 5,485,883 Rippetoe describes a method and apparatus to facilitate the economical recovery of crude oil from an oil well having a string of tubing which extends to the level of the underground reservoir of crude oil. Here an Ion Collider is attached to the lower end of the tubing in contact with crude oil in a crude oil reservoir. The Ion Collider apparatus consists of two spaced-apart cylindrical metal tubes whose common vertical axis coincides with the axis of the string of tubing. The collider's inner tube has its upper end capped and its lower end joined to the lower end of the outer tube whose upper end opens into the interior of the tubing, whereby the inner tube contains a multiplicity of spaced-apart holes in its cylindrical wall. The entire inner tube and the inner surface of the outer tube are made of an alloy of copper and nickel in which the copper comprises at least 80% of the alloy.
In U.S. Pat. No. 5,538,081 Rippetoe describes the use of a collider to facilitate the recovery of hydrocarbons from an underground reservoir. Here the collider is used to produce a quantity of negatively charged water which is then injected down an oil well and into the underground reservoir. Then a quantity of particles of a copper-nickel-zinc alloy are pumped down the oil well and into the underground oil reservoir. Optionally the alloy is followed by a quantity of frac sand pumped down the well and into the reservoir and followed by a sufficient volume of negatively charged water to flush the frac sand out of the well casing and wellbore and into the reservoir. The well is then shut-in to stabilize the particles of alloy and frac sand, if added, within the reservoir. The well is then reopened, allowing the water and gases formerly entrained within the reservoir to be expelled from the reservoir and the well, thereby leaving the alloy particles and frac sand, if used, within the reservoir to provide a path for the continuing flow or hydrocarbons to the wellbore.
Rippetoe further describes the use of a collider as part of a clarification system to purify water in U.S. Pat. No. 5,554,301. Here the system comprises a collision chamber having an entry aperture and an ion collider disposed in a central region therein. The ion collider reportedly treats the water and the contaminants with a plurality of free electrons. A separation chamber is disposed rearwardly of the collision chamber and is in flow communication with a first overflow weir for receiving the treated water and treated contaminants. An upstanding member in the separation chamber has a plurality of apertures sized to urge passage of the bulk of the treated contaminants through the apertures. A clarifying chamber is disposed rearwardly of the separation chamber and has a plurality of baffle plates obliquely oriented that urge upward flow of the treated water therethrough across the baffle plates. A water collection reservoir is disposed rearwardly of the clarifying chamber and is in flow communication with the clarifying chamber. A contaminant collection tank is disposed rearwardly of the water collection reservoir and is adapted with a contaminant receiving aperture that is in flow communication with a contaminant withdrawal trough in the clarifying chamber.
In still another related U.S. Pat. No. 6,036,849, Rippetoe describes a method of using a collider to remove hydrocarbons from soil and fluids. Here a collider is used to produce ionized water and the ionized water is mixed with the soil to facilitate the separation of the hydrocarbons from the soil.
As shown by the above patents, ion colliders appear to be a promising new fluid treatment and purification technology. Ion Colliders are reportedly able to ionize water and other fluids, producing reactive peroxide and hydroxyl compounds that readily oxidize undesirable contaminants or neutralize the opposing charges on solid contaminants, allowing them to be more easily removed by precipitation and filtration. In practice, however, ion colliders have been plagued by poor performance and variable results when used in commercial applications.
The poor and variable performance of ion colliders appears to be a function of the design, materials of construction and operation of the collider apparatus. In operation, colliders designed as described by Rippetoe in U.S. Pat. Nos. 5,482,629 and 6,106,787 often fail to generate true cavitation conditions within the fluids pumped through the holes in the inner chamber of the apparatus. Liquids pumped through the orifices may not cavitate or may cavitate in an uncontrollable manner so that the cloud of vapor bubbles fail to collapse at the catalytic surface. Uncontrolled cavitation that occurs in this manner is not effective as catalyzed cavitation and may fail to produce reactions at the copper-nickel catalyst surfaces.
In the Rippitoe apparatus, a significant gap of around 1.5 inches exists between the inner tube containing the orifices that project the liquid jet stream and the inner catalytically active wall of the outer tube. In practice, the gap would be filled with fluid which would have a tendency to diffuse, suppress and collapse any bubbles formed in the jet stream that exits from the orifices of the inner tube before the bubbles reach the catalytically active metal surfaces. Here the zone of cavitation would have too short of a life and thus would not generate the high temperatures and high pressures in the presence of a critical amount of the catalyst that are required to effectively change the physical and chemical properties of the fluids in a manner to efficiently separate contaminants and purify the fluid. Addition of a helix of wire made from catalytically active materials that is wound around the circumference of the inner pipe does not appear to be able to improve contact between the bubble cloud and the catalyst surface.
Impingement of a fluid without cavitation may not be sufficient to ionize a fluid in the Rippetoe collider. Simple impingement of a liquid jet stream against a copper-nickel surface in the absence of cavitation adjacent to that surface should not strip copper ions away from the surface. Copper-nickel alloys and copper-nickel metals are reported to have the highest corrosion resistance of all copper alloys and are particularly resistant to corrosion caused by fluid impingement. (Perry's Chemical Engineer's Handbook, 6th Edition 1984, McGraw-Hill). The addition of small amounts of zinc or silver would not have a particularly destabilizing effect upon the integrity of the alloy surface in the absence of true cavitation.
The Rippetoe inventions also appear to be too inflexible to be able to treat and condition a wide variety of fluids under a wide variety of process conditions. The Rippetoe patents specify a limited variety of catalytic surfaces and a simplified orifice structure for cavitating the fluid that would have a limited ability even in theory to catalyze a wide range of cavitation-induced reactions.
Accordingly, there is a need for a new method of and apparatus for utilizing hydrodynamic cavitation as an effective and low cost fluid treatment and conditioning process.
There is also a need for a method of removing impurities, including sulfur, from fluids including hydrocarbons and fuels and for re-mediating soil with minimal use of chemical treatment.
There is also a need to separate oil from aqueous fluids and break apart oil-in-water emulsions without the use of chemicals, clarifiers or coalescers.
There is also a need to purify water and to remove of dissolved solids from fluids, de-scale pipes and vessels, and condition fluid without the use of chemicals.
In addition, there is a need for a device and apparatus so constructed to employ catalyzed hydrodynamic cavitation in a controllable process to economically purify water and other fluids at low operating cost and moderate equipment cost compared to other fluid treatment processes.